weight the front. ie 4000lb on the front... 2000 a corner. rought that is you loaded ride hieght
pending lenght of hte srping depics you spring ratings
14" 500lb/in spring will compress 4" for the load
a 10" 1000lb/in will compress 2"
pic the shock
find what lenght spring works with it
figuer out were you what ride hieght to be on the shock.. ie 10" stroke 5" ride hieght give you 5" of droop and 5" of compression.
thats this gist of it.. can get in to more detials
That will only get you so close, and I'm a little rusty at it so take this post with a grain of salt. :rofl:.
You have to figure in the lever arm, or the amount of leverage the suspension has on the spring.
A quick example is that if your a-arm is 24" from pivot to tire cl and your shock is 1/2 way between you will get 4" of suspension travel for 2" of spring travel You would then need to double your calculated spring rate to compensate. Now that I've hopefully got you understanding this a little I'll throw a curve ball at you.
If the spring is mounted at anything except a 90 degree angle to the travel of the lever arm it will change the rate needed also.
It can work out at all different kinds of weird rates. When you start dealing with the shock on the other side of the tire CL and an instant center on the suspension that can be moved around it can really get interesting.
Best advice is to check the return policy before you buy the springs. You may need to change them a time or two to dial them in perfectly.